A PEDAGOGICAL VIEW ABOUT THE DESIGN OF ISOXAZOLYL-PENICILLINS OF THE AMPC BETALACTAMASE RECEPTOR 1FCM USING THE DOCKING MOLECULAR TECHNIQUE UNA MIRADA PEDAGOGICA SOBRE EL DISEÑO DE ISOXAZOLIL-PENICILINAS DEL RECEPTOR 1FCM DE LA BETALACTAMASA AMPC EMPLEANDO LA TÉCNICA DE ACOPLAMIENTO MOLECULAR

The present work mainly exposes the result of the search for molecules, derived from the structural changes of the drug Cloxacillin in its phenyl radical, which is chlorinated, likewise, the selection of the pharmacophore group is evidenced, which allowed to specify the aforementioned objective. Secondly, the selected target was beta-lactamase, with 1FCM nomenclature, registered in the database, Protein Data Bank, in the same way, the amino acids involved in non-covalent interactions are found, in this order of ideas, they were raised, 22 molecules that presented an affinity energy lower than -8.0 Kcal/mol, this data stated above, will become the reference value, to postulate 6 molecules that have registered a lower affinity, generated by the Autodock Vina software. To conclude, the structural optimization of the leading drug is given as a result, together with its new interactions in the amino acids LYS64, ASN149, THR313 and SER61.


INTRODUCTION
The history of mankind has been characterized mainly by discoveries that have an immediate or future utility. This premise is evident in the discovery of penicillin, which is attributed to Alexander Fleming (Fleming, 1929). Penicillin would give way to the new family of drugs called beta-lactams. After about 70 years, beta-lactams have become the most prescribed antimicrobials in clinical treatments against bacterial strains such as Streptococcus pneumoniae (Ruvinsky, 2001).
Despite the fact that no really new betalactam has been available for more than 2 decades, the incessant increase in resistance and the advances in the knowledge of its molecular mechanisms, has conditioned the existence of a large amount of information in the medical literature on each of the components of this family of antibiotics (Cantón & Horcajada, 2013).
In this order of ideas, it is possible to establish that beta-lactams are antibiotics, which are mainly characterized by inhibiting the last stage of bacterial cell wall synthesis. Their action is slow, depends only on time, and has very low toxicity (Choque, 1993).

JUSTIFICATION
The β-lactams have been characterized by their success in the treatment of bacterial infections; however, bacterial resistance has become a limiting factor to perform effective treatments in new infected patients; consequently, there is a demand to develop new beta-lactams that allow overcoming the challenge of bacterial resistance. The main objective of this scientific article is to show the results of the Isoxazolylpenicillin design of the 1FCM receptor of the beta-lactamase ampc using the molecular docking technique. In this order of ideas, it will be necessary to make structural modifications to Cloxacillin, in other words, to add atoms or functional groups that increase/intensify the drug-target interactions.

FAMILY
The structural identification of the betalactam family is evidenced by the presence of the beta-lactam ring, which, in turn, defines the chemical characteristics of this family as shown in Figure 1. is not present in the eukaryotic animal cell) and the main mechanism of resistance (betalactamases) of this large family of antibiotics. It should be noted that for the beta-lactam to be active, it must be bound to other radicals (usually other rings). The modifications of the properties of the resulting compound are not only mediated by the basic skeleton, which is formed by the 2 rings (called nucleus), but also by the union of different types of linear chains, to give way to the general classification of beta-lactam antibiotics: penicillins, cephalosporins, carbapenemics, monobactams and beta-lactamase inhibitors (Cué & Morejón, 1998).
In other words, it is possible to establish that, within each group, small alterations in the chemical structure are capable of modifying the characteristics of the antibiotic, such as spectrum, affinity for certain receptors or resistance to beta-lactamases (Cué & Morejón, 1998).
In summary, this first section highlights the importance of making structural modifications, preferably in silico or through computer-assisted molecular modeling, for subsequent testing, · 1 2 4 · either in antibiograms or in patients with bacterial infection.

MECHANISM OF ACTION OF BETA-LACTAMS
It is necessary to emphasize that beta-lactam antibiotics are considered as bactericidal agents, which have 2 mechanisms of action: 1) To inhibit the synthesis of the bacterial wall 2) To induce bacterial autolysis (Livermore, 1993). Because of this, it is necessary to take into account that the bacterial wall is a structure that covers bacteria of all genera, except for mycoplasmas; it is located outside the cytoplasmic membrane and is mainly composed of a protein called peptidoglycan (Curtis & Schnek, 2008).  The last phase in the conformation of the cell wall, has as its objective, the formation of tetrapeptides, taking as a starting point the pentapeptides, demanding the presence of enzymes in the periplasmic space, which are commonly known as transpeptidases (Garcia et al., 2014).
In summary, without the presence of the cell wall, the microorganism will be exposed to the environment, generating a death due to changes in the oncotic pressure, however, for there to be an effective pharmacological action by the beta-lactams, it is essential that the bacteria is still in the multiplication phase, since this is the time when bacteria perform the synthesis of their cell wall (García, Castillo & Salazar, 2014). In view of the absence of the cell wall, beta-lactams activate an endogenous bacterial autolysin, which disintegrates the peptidoglycan, sometimes strains of bacteria do not present autolysin, which are usually tolerant to betalactams, this means that they inhibit their growth with the presence of the beta-lactam group, but present a complete lysis (Agudelo et al., 2009). and Staphylococcus epidermidis (Lipman, 1993). Dicloxacillin.

CHARACTERIZATION OF CLOXACILLIN
Cloxacillin is part of the beta-lactam family, which presents the characteristic beta-lactam ring, it is also formed by four members, one of these, an amine group, together with a keto group, which gives it a very important polarity in terms of the intermolecular interactions to be performed, as in this case, the interactions with the selected target (1FCM).

DESCRIPTION OF CLOXACILLIN
Cloxacillin ( Figure 4C) is a molecule that is made up of 9 Heteroatoms, which can be grouped as, Chlorine, Nitrogen and Oxygen; Cloxacillin, is characterized by presenting the characteristic ring of the beta-lactam family, it is identified by forming a four-membered ring that is joined to a 5-membered ring, in which the Nitrogen heteroatom is located (Gomez et al., 2015).
It is considered as a beta-lactam antibiotic.
It inhibits the synthesis of the bacterial cell wall through the non-covalent coupling or binding of one or more Penicillin-binding proteins (e.g. carboxypeptidases, endopeptidases, transpeptidases) in the periplasmic membrane.
As it happens in the great majority of beta-lactams, B O L E T Í N R E D I P E 1 0 ( 9 ) : 1 2 1 -1 3 7 -S E P T I E M B R E 2 0 2 1 -I S S N 2 2 5 6 -1 5 3 6 · 1 2 6 · the studied drug blocks the final transpeptidation step of peptidoglycan synthesis. The cell dies by the action of autolytic enzymes (Autolysins and Murein hydrolases) after exposure to the betalactam antibiotic (Sharon, 2007).

WHEN AND BY WHOM WAS IT DISCOVERED?
Interestingly, the commercial molecule

PHARMACOPHORE GROUP
Determining a pharmacophore is the most relevant first step in understanding the interaction between a receptor and a ligand. In the early 1900s, Paul Ehrlich postulated that a pharmacophore is conceived as "A molecular fragment that presents (Phoro) the essential characteristics responsible for the biological activity of a drug" (Güner et al 2000). This premise has been valid for more than 60 years; however, the current definition presented by Peter Gund in 1977 established that: "A pharmacophore is a set of structural characteristics of a molecule that is recognized at a receptor site and is responsible for the biological activity of that molecule" (Güner et al, 2000).
At this point, mention is made of the pharmacophore group selected for Structure-Based Virtual Screening:  for the selected drug.
The molecular coupling demands to perform optimizations in its 3D structure, in this order of ideas, this optimization with respect to the drug Cloxacillin, will be mediated by two main free download software, these are Avogadro and ChemDraw, the first will be based on performing energy optimization regarding its molecular spatial structure, however to optimize this criterion, the drawing was first performed in a single plane or planar structure, in ChemDraw software, which was subsequently recorded

COMPUTATIONAL PHASE
The first criterion to perform the virtual screening was the affinity energy, which is one of the results of the molecular docking and which is specific to the algorithm of the different softwares. It is established that the affinity energy is part of the scoring functions "which are force fields based on molecular mechanical physics that estimate the energy of the pose; a low (negative) energy indicates a stable system and, therefore, a probable binding interaction" (Gaba et al., 2010). (Gaba et al., 2010). From the literature it means that the lower the calculated affinity energy the higher the probability of a ligand-protein interaction.
Therefore, by molecular docking the resulting affinity energy of Cloxacillin against the 1FCM receptor is (-8.0 Kcal/mol). We started from this ligand making structural changes to establish a lower free energy. Continuing with this premise, 55 molecules were designed, where only 6 of them (Table 4)   Of the 6 molecules raised in Table 4, only 4 showed interactions smaller than 3.0 Å in reference to the amino acid GLU147, this would indicate a higher probability of interaction between ligand and receptor (Fu, Zhao, & Chen, 2018). In view of the interactions found, it is possible to affirm that the amino acid GLU147, is responsible for the anchoring, as observed in   growth. The variable being tested is the ability of the mutagens to cause a reversion to growth in a medium without histidine. (Bruce et al., 1973). antibiotics, leading to drug resistance. (Kumar, Anbarasu & Ramaiah,2014).
At this point we have molecule N°1 (Table   4)

CONCLUSIONS
The design of 55 structures allowed us to propose 6 molecules with an acceptable affinity compared to the leading molecule, which, in this case, was Cloxacillin, as a result of structural modifications made in the region of the chlorinated phenyl group.
The design of Isoxazolyl-penicillins of the 1FCM receptor of the beta-lactamase ampc, which presented an increase in ligand-receptor affinity, was successfully carried out using the molecular docking technique.
As a result of the structural optimization of the lead drug, a lower free energy was evidenced in the proposal of molecule N°1 recorded in